Dengue and chikungunya viruses, causative agents of the globe's two most important arboviral diseases, are transmitted to humans predominantly by the widespread invasive mosquitoes, Aedes aegypti and Aedes albopictus. Following its broad diaspora during the last three decades from Asia, A. albopictus has established in new continents and countries where its invaded distribution often overlaps that of A. aegypti, originally native to Africa. Many recent invasions by A. albopictus have led to reductions, sometimes quite rapidly, in abundance and range of previously established A. aegypti. Despite the potential impacts of such displacements on arbovirus epidemiology, our current understanding of causative mechanisms is inadequate to explain the observed patterns of rapid reductions of A. aegypti populations. This application resurrects and tests a neglected potential mechanism, asymmetric reproductive interference, based on new preliminary results which show that (1) A. albopictus and A. aegypti mate at sites of sympatry in south Florida and (2) heterospecific male accessory gland products, transferred during mating, sterilize A. aegypti, but not A. albopictus, females. Experiments and observations are proposed to strengthen understanding how reproductive interference, of a type known as satyrization, may lead to the observed rapid displacements of A. aegypti by A. albopictus. A major thrust of this research tests whether allopatric populations of A. aegypti are more susceptible to satyrization than populations with a history of sympatry with A. albopictus. Important to future research on this subject, the application will improve and expedite the molecular diagnostic tools used to detect heterospecific matings in nature and experimentally in outdoor cages. Employing sympatric and allopatric populations of the two species which occur naturally in Florida, Aim #1 will test in large outdoor cages the hypothesis that A. aegypti which have been geographically isolated from A. albopictus will be more susceptible to heterospecific matings. Varying relative abundances of recent Florida colonies of the two species in outdoor cages, Aim #2 will validate a satyrization model and quantify how encounter frequency determines the incidence of heterospecific matings. Taking advantage of collaborators who will assist with collections in Asia, Africa, and South America, Aim #3 will test the hypothesis that the frequency of heterospecific mating between A. albopictus and A. aegypti is inversely proportional to the time since sympatry of natural or invaded populations.